1. Field of the Invention
This invention relates to a system and method for selectively compressing and dispensing methane, hydrogen and variable mixtures of methane and hydrogen, preferably for vehicular refueling applications. The use of methane in the form of natural gas is preferred.
2. Description of Related Art
Systems and methods for compressing fuel gas and for refilling vehicle storage tanks with fuel gas are disclosed, for example, in U.S. Pat. Nos. 5,351,726; 5,538,051; 5,628,349; and 5,694,985. Such systems are presently being used in many locations to provide clean-burning compressed natural gas (“CNG”) for use in private and commercial vehicles.
During recent years, there has been growing interest in the use of hydrogen as an alternative fuel. While the increased use of hydrogen as a vehicular fuel gas will reduce the depletion rate of naturally occurring hydrocarbons and also reduce hydrocarbon emissions into the atmosphere, it also presents new problems. First, because hydrogen is significantly less dense than natural gas at atmospheric conditions, it must be compressed to higher pressures than natural gas in order to force a sufficient amount into a vehicular fuel tank to achieve a satisfactory operating range before refueling. Second, because hydrogen must be compressed to such high pressures for effective refueling, the time required for refueling can be longer than is practicable for everyday vehicular use.
Also, the effective implementation of either CNG or hydrogen refueling systems requires a sufficient number of refueling stations to make the fuel readily available to users who live and drive over a widespread geographical area. This can become prohibitively expensive if separate stations are required for the different fuels, or even if different stand-alone compression and dispensing systems are required in order to make either CNG or hydrogen available at a single station location.